全文获取类型
收费全文 | 5520篇 |
免费 | 620篇 |
专业分类
系统科学 | 1073篇 |
理论与方法论 | 275篇 |
现状及发展 | 876篇 |
研究方法 | 20篇 |
综合类 | 3890篇 |
自然研究 | 6篇 |
出版年
2020年 | 1篇 |
2018年 | 728篇 |
2017年 | 732篇 |
2016年 | 430篇 |
2015年 | 30篇 |
2014年 | 3篇 |
2013年 | 2篇 |
2012年 | 271篇 |
2011年 | 959篇 |
2010年 | 814篇 |
2009年 | 454篇 |
2008年 | 518篇 |
2007年 | 769篇 |
2006年 | 13篇 |
2005年 | 49篇 |
2004年 | 126篇 |
2003年 | 153篇 |
2002年 | 58篇 |
2001年 | 1篇 |
2000年 | 2篇 |
1994年 | 2篇 |
1992年 | 1篇 |
1991年 | 3篇 |
1984年 | 2篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1975年 | 5篇 |
1973年 | 1篇 |
1972年 | 2篇 |
1971年 | 1篇 |
1969年 | 1篇 |
1968年 | 1篇 |
1967年 | 1篇 |
1966年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有6140条查询结果,搜索用时 15 毫秒
941.
This paper considers the problem of minimizing the VaR and CTE of an insurer’s retained risk by controlling the combinational
quota-share and stop-loss reinsurance strategy. With a constrained reinsurance premium, the authors give the explicit reinsurance
forms and the minimal VaR and CTE of retained risk in the case of quota-share after stop-loss reinsurance and the case of
stop-loss after-quota-share reinsurance respectively. Finally, the authors conclude that the quota-share after stop-loss is
a better reinsurance strategy than stop-loss after quota-share to minimize the VaR and CTE with a same constrained reinsurance
premium. And the pure stop-loss reinsurance is preferred for an insurer with a high level regulatory requirement. 相似文献
942.
The objective of this paper is to study the issue of design efficiency for minimum projection uniformity designs. The results
show that for orthogonal arrays with strength two, the minimum projection uniformity criterion is a good surrogate for the
design efficiency criterion proposed by Cheng, Deng and Tang (2002). 相似文献
943.
This paper discusses the H
∞ control problem for a class of linear stochastic systems driven by both Brownian motion and Poisson jumps. The authors give
the basic theory about stabilities for such systems, including internal stability and external stability, which enables to
prove the bounded real lemma for the systems. By means of Riccati equations, infinite horizon linear stochastic state-feedback
H
∞ control design is also extended to such systems. 相似文献
944.
Preventing rumor spreading on small-world networks 总被引:1,自引:0,他引:1
Since the spreading of harmful rumors can deeply endanger a society, it is valuable to investigate strategies that can efficiently
prevent hazardous rumor propagation. To conduct this investigation, the authors modify the SIR model to describe rumor propagation
on networks, and apply two major immunization strategies, namely, the random immunization and the targeted immunization to
the rumor model on a small-world network. The authors find that when the average degree of the network is small, both two
strategies are effective and when the average degree is large, neither strategy is efficient in preventing rumor propagation.
In the latter case, the authors propose a new strategy by decreasing the credibility of the rumor and applying either the
random or the targeted immunization at the same time. Numerical simulations indicate that this strategy is effective in preventing
rumor spreading on the small-world network with large average degree. 相似文献
945.
A general complex delayed dynamical network model with asymmetric coupling matrix is considered in this paper. For reducing
the conservativeness of synchronization criteria, several novel synchronization stability conditions are presented by using
delay decomposition methods. Numerical examples which are widely used to study delay-dependent synchronization stability are
given to illustrate the effectiveness of the proposed methods. 相似文献
946.
José Afonso de Oliveira Amarildo Jorge da Silva 《Systemic Practice and Action Research》2011,24(6):565-574
The context of this analysis is the golden years of the decade of the 1960s that served as a backdrop for consolidating capitalism
and the globalized world. The aim is to analyze, understand and establish possible connections between the arts in general
and the world in which modern society operates. This is a theoretical essay anchored in theoretical assumptions of sociology,
arts and the culture of the globalized world and built on the practical experience of these researchers. We use the interpretative
approach and technique of hermeneutic phenomenology to give meaning to historical events and the cultural and artistic implications
of these events in the rise of science and technology. A systemic examination supports the relationship between art, culture,
science and technology. The evidence shows that artistic and cultural issues are essential to make sense of life in society
and in the absence of such basis, the world would be meaningless and humans would lose a sense of direction. It can be concluded
that the arts are becoming increasingly relevant as the virtual world becomes large-scale and truly global, and that the development
of science and technology benefits from the rise of the cultural and artistic world of today. Finally, the correspondence
between the artistic and cultural world and the current scientific and technological development confirms the emergence of
a globalized, digitalised (virtual) knowledge society. 相似文献
947.
This paper defines a new class of generalized type I functions, and obtains Kuhn-Tucker necessary and sufficient conditions
and duality results for constrained optimization problems in the presence of the aforesaid weaker assumptions on the objective
and constraint functions involved in the problem. 相似文献
948.
This study aims to reduce the statistical uncertainty of the correlation coefficient matrix in the mean-variance model of
Markowitz. A filtering algorithm based on minimum spanning tree (MST) is proposed. Daily data of the 30 stocks of the Hang
Seng Index (HSI) and Dow Jones Index (DJI) from 2004 to 2009 are selected as the base dataset. The proposed algorithm is compared
with the Markowitz method in terms of risk, reliability, and effective size of the portfolio. Results show that (1) although
the predicted risk of portfolio built with the MST is slightly higher than that of Markowitz, the realized risk of MST filtering
algorithm is much smaller; and (2) the reliability and the effective size of filtering algorithm based on MST is apparently
better than that of the Markowitz portfolio. Therefore, conclusion is that filtering algorithm based on MST improves the mean-variance
model of Markowitz. 相似文献
949.
Endo-β-glucanases play vital roles in the regulation of pollen tube growth. Here, a previously identified endo-l,4-β-glucanase from Lilium Iongiflorum (lily), named LlpCell, was expressed in Escherichia coli, purified, and further investigated for its physiological function. The recombinant LlpCell protein hydrolyzed carboxy-methylcellulose (CMC) and exhibited activity towards laminarin from Eisenia. arborea and 1,3:l,4-β-glucan of barley. The pH for the optimum activity was 6.0 and the value of Km calculated from CMC was 5.0 mg/mL. Adding EDTA resulted in the total loss of the enzymatic activity, and this effect could be restored by the addition of Ca^2+. Western blotting analysis showed that LlpCell protein was present in pollen grains and rehydrated pollen grains, and the amount of the protein was increased during pollen germinating, but not in the pollen tube. Consistently, the immunofluorescence labeling study with the antibody against LIpCell also indicated the presence of LIpCell at the begin-ning of germination, but not in the elongating pollen tube. Furthermore, incubation of LlpCell with pollen at the beginning of pollen germination increased the germination percentage and the length of pollen tube. All of these results suggested that LlpCell could play an important role in the regulation of lily pollen germination and the initiation of pollen tube growth. 相似文献
950.
We demonstrated a two-dimensional quasi-crystal dendritic structure model with negative permeability. The microwave transmission and reflection properties of periodic and quasi-crystal dendritic structure mediums with varied angle incidence were measured. The results showed that the resonant peaks of quasi-crystal negative permeability samples and left-handed samples had tiny shift with the altering of incident angle. Because of the influence of coupling between quasi-crystal dendritic cells, the resonance of the entire material was enhanced or weakened. The quasi-crystal dendritic structure model will provide an easy method to design isotropic left-handed materials (LHMs). 相似文献